How garbage is turned into energy

One of the first successful waste-to-energy plants built in the United States was a $46 million facility constructed on a former landfill site in a tidal marsh north of Boston.

The facility, owned and operated by Signal RESCO Inc., burns about 1,200 tons of garbage a day. It works like this:

Garbage trucks dump their loads into a giant holding area. Garbage - ranging from egg shells and paper plates to old ovens and car tires - is loaded by crane into the furnace. The garbage slides slowly down a slanted grate into the 2,500 -degree F. furnace. The flames are fed a steady gust of fresh air from giant fans that also serve to circulate the air in the garbage holding area.

The furnace walls are lined with steel pipes filled with water. As the water is converted to steam, it is used to turn electric generators or is routed as pressurized steam to industrial users.

Smoke from the furnace is partially cooled in the steammaking process and then is channeled through an electrostatic precipitator that chemically ''scrubs'' the smoke particles, reducing industrial emissions to within acceptable environmental standards.

Meanwhile, the ash, metal, or other nonflammable remains of the garbage eventually fall into a cooling tank. They are lifted by conveyor out of the plant. The residue is divided into metal scrap and ash. The ash is dumped by truck in a landfill. Scrap is either stockpiled or sold.